Cyclotridecanone 2,4-dinitrophenylhydrazone.

In cyclotridecanone 2,4-dinitrophenylhydrazone, C(19)H(28)N(4)O(4), the 13-membered carbocycle exists in the triangular [337] conformation. The 2,4-dinitrophenylhydrazone group is almost perpendicular to the 13-membered ring, with a dihedral angle of 82.66 (2) degrees between the mean planes.

Cyclopentadecanone 2,4-dinitrophenylhydrazone.

In the title compound, C(21)H(32)N(4)O(4), no disorder is present in the 15-membered hydrocarbon ring, which exists in an unsymmetrical quinquangular [12345] conformation. The 2,4-dinitrophenylhydrazone group is approximately perpendicular to the C(15) ring, with a dihedral angle of 84.66 (1) degrees between their best planes.

Cyclopentadecanone.

In the crystal structure, the title compound (exaltone), C(15)H(28)O, exhibits no disorder, and the 15-membered ring exists in the quinquangular [13353] C(1) symmetry conformation. The crystal exhibits nonmerohedral twinning by twofold rotation about [100], but adjustment of the temperature to 90 K causes the [101] distance to equal the c axial length, allowing the twinning to be treated as pseudo-merohedral. The literature description of the structure as disordered orthorhombic with halved a-axis length is corrected.

Conformational equilibria in formic acid and the adduct of formic acid and hexafluoroacetone, HCO2C(CF3)2OH.

Low-temperature 1H and 13C NMR spectra of formic acid (1) showed separate signals for the E and Z conformations in solvents containing a hydrogen bond acceptor, dimethyl ether. The population of E-1 (6.2% in 3:1:1 CHClF2/CHCl2F/(CH3)2O) was larger than that for 13C-labeled methyl formate in the same solvent (0.

Interconversion of carbon sites in boat-chair-boat cyclodecane; conformations of chlorocyclodecane and cyclodecyl acetate.

Interconversion of carbon sites in boat-chair-boat (BCB) cyclodecane occurs by way of the twist-boat-chair (TBC) conformation, which predicts that C-1 exchanges with C-4, etc. The previously obtained low-temperature 13C spectra could be matched by assuming (1,4) or (1,3) exchange, but not (1,2) exchange. A free-energy barrier of 5.

Cyclodecyl 4-nitrophenylacetate.

Cyclodecyl 4-nitrophenylacetate, C18H25NO4, has its ten-membered ring in the expected diamond-lattice boat-chair-boat [2323] conformation, with the substituent 4-nitrophenylacetoxy group in the BCB IIIe position. The ester unit has the expected Z conformation, with an O=C-O-C torsion angle of -0.3 (3) degrees, and the connection to the benzene ring is nearly perpendicular to the ester, with an O=C-C-C torsion angle of 85.

Conformations of cycloundecane.

Cycloundecane (1) was shown to exist at -183.1 degrees C as a mixture of the [12323] (approximately 59%) and [335] (approximately 41%) conformations. Populations were determined from the (13)C NMR spectrum, and assignments were based on the (13)C spectra, calculated free energies and chemical shifts, and information from the literature, including X-ray studies of solid derivatives and calculated barriers.

Conformational study of cis-1,4-di-tert-butylcyclohexane by dynamic NMR spectroscopy and computational methods. Observation of chair and twist-boat conformations.

[reaction: see text] Low-temperature 13C NMR spectra of cis-1,4-di-tert-butylcyclohexane (1) showed signals for the twist-boat (1a) and chair (1b) conformations. 13C NMR signals were assigned to specific carbons based on the different populations, different symmetries (time-averaged C(2v) for 1a and time-averaged C(s) for 1b), and calculated chemical shifts (GIAO, HF/6-311+G*). In addition to slow ring inversion and interconversion of the chair and twist-boat conformations, slow rotation of the tert-butyl groups was found.

Conformational study of 1,2-cycloundecadiene by dynamic NMR spectroscopy and computational methods.

Solutions of 1,2-cycloundecadiene in propane were studied by low-temperature (13)C NMR spectroscopy. A total of 17 peaks were observed at -166.7 degrees C, corresponding to two conformations of similar populations, one of C(1) symmetry (11 peaks) and the other of C(2) symmetry.

Conformational Study of Oxacyclooctan-2-one by Dynamic NMR Spectroscopy and Computational Methods.

The slow-exchange (13)C NMR spectrum of the eight-membered lactone, oxacyclooctan-2-one (1), at -154.2 degrees C shows the presence of two conformations with populations of 25.6 and 74.

Conformational Study of trans-Cyclododecene by Dynamic NMR Spectroscopy and Computational Methods.

The (13)C spectrum of trans-cyclododecene (1) dissolved in propane showed seven peaks for the olefinic carbons at -164.5 degrees C, corresponding to three conformations of C(1) symmetry and a fourth conformation, with a population of 20.1%, of C(2) symmetry.